CTRL + A Menu Apply Transformation : where to find in Python document
For this one ( or other shortcuts ) :


go to User File -> preferences -> Input 
search for a key combination  "Ctrl  A"
expand the shortcut for "call menu" under "Object mode"
you can see the command is "wm.call_menu" and the name attribute is "VIEW3D_MT_object_apply"


since the shortcut point to an operator which should be under "bpy.ops", we use this line to call the same menu  :

bpy.ops.wm.call_menu(name="VIEW3D_MT_object_apply")